"Sonochemistry" in Comprehensive Coordination Chemistry 2

1.41
CCC.0005 Sonochemistry
K. S. SUSLICK
University of Illinois at Urbana-Champaign, Urbana, IL, USA
1.41.1 INTRODUCTION 1
1.41.1.1 Acoustic Cavitation 2
1.41.1.2 Microjet Formation During Cavitation at Liquid–Solid Interfaces 3
1.41.2 SONOLUMINESCENCE 4
1.41.2.1 Types of Sonoluminescence 4
1.41.2.2 Spectroscopic Probes of Cavitation Conditions 5
1.41.3 SONOCHEMISTRY 5
1.41.3.1 Homogeneous Sonochemistry: BondBreaking andRadical Formation 6
1.41.3.2 Applications of Sonochemistry to Materials Synthesis 6
1.41.3.3 Heterogeneous Sonochemistry: Reactions of Solids with Liquids 7
1.41.4 CONCLUSIONS 9
1.41.5 REFERENCES 9
SECCCC01046.1.41.1 1.41.1 INTRODUCTION
01046
CCC01046.0010 Ultrasonic irradiation of liquids causes high-energy chemical reactions to occur, often with the
emission of light.[bib1 bib2 bib3] 1–3 The origin of sonochemistry andsonoluminescence is acoustic
cavitation: the formation, growth, andimplosive collapse of bubbles in liquids irradiatedwith
high-intensity sound. The collapse of bubbles caused by cavitation produces intense local heating
andhigh pressures, with very short lifetimes. In clouds of cavitating bubbles, these hot-spots[bib4
bib5 bib6] 4–6 have equivalent temperatures of roughly 5,000 K, pressures of about 1,000 atm, and
heating andcooling rates above 10 10 Ks 1 . In single bubble cavitation, conditions may be even
more extreme. Thus, cavitation can create extraordinary physical and chemical conditions in
otherwise coldliquids.
CCC01046.0015 When liquids that contain solids are irradiated with ultrasound, related phenomena can occur.
When cavitation occurs near an extended solid surface, cavity collapse is non-spherical and drives
7
high-speedjets of liquidinto the surface. [bib7] These jets andassociatedshock waves can cause
substantial surface damage and expose fresh, highly heated surfaces. Ultrasonic irradiation of
liquid–powder suspensions produces another effect: high-velocity inter-particle collisions. Cavitation
andthe shockwaves it creates in a slurry can accelerate solidparticles to high velocities.[bib8] 8
The resultant collisions are capable of inducing dramatic changes in surface morphology, composition,
andreactivity.[bib9] 9
CCC01046.0020 Sonochemistry can be roughly divided into categories based on the nature of the cavitation
event: homogeneous sonochemistry of liquids, heterogeneous sonochemistry of liquid–liquid or
liquid–solid systems, and sonocatalysis (which overlaps the first two). In some cases, ultrasonic
irradiation can increase reactivity by nearly a million-fold.[bib10] 10 Because cavitation can only
occur in liquids, chemical reactions are not generally seen in the ultrasonic irradiation of solids or
solid–gas systems.
CCC01046.0025 Sonoluminescence in general may be considered a special case of homogeneous sonochemistry;
however, recent discoveries in this field have heightened interest in the phenomenon in and by
1

2 Sonochemistry
itself.[bib11 bib12] 11,12 Under conditions where an isolated, single bubble undergoes cavitation,
recent studies on the duration of the sonoluminescence flash suggest that a shock wave may be
createdwithin the collapsing bubble, with the capacity to generate truly enormous temperatures
andpressures within the gas.
secCCC01046.1.41.1.1 1.41.1.1 Acoustic Cavitation
CCC01046.0030 The chemical effects of ultrasound do not arise from a direct interaction with molecular species.
Ultrasoundspans the frequencies of roughly 15 kHz to 1 GHz. With soundvelocities in liquids
typically about 1,500 m s 1 , acoustic wavelengths range from roughly 10 to 10 4 cm. These are not
molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species
on a molecular level can account for sonochemistry or sonoluminescence.
CCC01046.0035 Instead, sonochemistry and sonoluminescence derive principally from acoustic cavitation,
which serves as an effective means of concentrating the diffuse energy of sound. Compression
of a gas generates heat. When the compression of bubbles occurs during cavitation, it is more
rapidthan thermal transport, which generates a short-lived, localizedhot-spot. Rayleigh’s early
descriptions of a mathematical model for the collapse of cavities in incompressible liquids
predicted enormous local temperatures and pressures.[bib13] 13 Ten years later, Richards and
Loomis reportedthe first chemical andbiological effects of ultrasound.[bib14] 14
CCC01046.0040 If the acoustic pressure amplitude of a propagating acoustic wave is relatively large (greater
than 0.5 MPa), local inhomogeneities in the liquidcan give rise to the rapidgrowth of a
nucleation site into a cavity of macroscopic dimensions, primarily filled with vapor. Such a
bubble is inherently unstable, andits subsequent collapse can result in an enormous concentration
of energy ( [figCCC01046.1] Figure 1). This violent cavitation event is generally termed‘‘transient
cavitation.’’ A normal consequence of this unstable growth andsubsequent collapse is that the
cavitation bubble itself is destroyed. Gas-filled remnants from the collapse, however, may give rise
to reinitiation of the process.
CCC01046.0045 A variety of devices have been used for ultrasonic irradiation of solutions. There are three
general designs in use presently: the ultrasonic cleaning bath, the direct immersion ultrasonic
horn, andflow reactors. The originating source of the ultrasoundis generally a piezoceramic
material that is subjectedto a high AC voltage with an ultrasonic frequency (typically 15 to
50 kHz). The vibrating source is attachedto the wall of a cleaning bath, to an amplifying horn, or
to the outer surfaces of a flow-through tube or diaphragm. The ultrasonic cleaning bath is clearly
the most accessible source of laboratory ultrasoundandhas been usedsuccessfully for a variety of
liquid–solid heterogeneous sonochemical studies. The low intensity available in these devices
( 1Wcm 2 ), however, means that even in the case of heterogeneous sonochemistry, an ultrasonic
cleaning bath must be viewedas an apparatus of limitedcapability. The most intense andreliable
source of ultrasoundgenerally usedin the chemical laboratory is the direct immersion ultrasonic
Acoustic
pressure
Liquid
density
Bubble radius (mm)
150
100
50
+
–
Growth
Implosion
Shockwave (?)
Rapid
0
Formation
Hot spot quenching
0 100 200 300 400 500
Time (µs)
figCCC01046.1 Figure 1 Transient acoustic cavitation: the origin of sonochemistry andsonoluminescence.

Cooling
bath
Sonochemistry 3
Power supply
Piezoelectric
transducer
Titanium horn
Collar & O-rings
Gas inlet / outlet
Glass cell
Reaction
solution
figCCC01046.2 Figure 2 A typical sonochemical apparatus with direct immersion ultrasonic horn. Ultrasound can be easily
introduced into a chemical reaction with good control of temperature and ambient atmosphere.
horn (50 to 500 W cm 2 ), as shown in [figCCC01046.2] Figure 2, which can be usedfor work under
either inert or reactive atmospheres or at moderate pressures (

4 Sonochemistry
before ultrasound
100µm
heterogeneous reactions. The erosion of metals by cavitation generates newly exposed, highly
heatedsurfaces.
CCC01046.0065 A solidsurface several times larger than the resonance bubble size is necessary to induce
distortions during bubble collapse. For ultrasound of 20 kHz, damage associated with jet
formation cannot occur if the solidparticles are smaller than 200 m. In these cases, however,
the shockwaves createdby homogeneous cavitation can create high-velocity interparticle collisions.[bib8
bib9] 8,9 Suslick andco-workers have foundthat the turbulent flow andshockwaves
produced by intense ultrasound can drive metal particles together at sufficiently high speeds to
induce effective melting in direct collisions and the abrasion of surface crystallites in glancing
impacts ([figCCC01046.3] Figure 3). A series of transition metal powders were used to probe the
maximum temperatures and speeds reached during interparticle collisions. Using the irradiation
of Cr, Mo, and W powders in decane at 20 kHz and 50 W cm 2 , agglomeration andessentially a
localizedmelting occurs for the first two metals, but not the third. On the basis of the melting
points of these metals, the effective transient temperature reachedat the point of impact during
interparticle collisions is roughly 3,000 C (which is unrelatedto the temperature inside the hotspot
of a collapsing bubble). From the volume of the meltedregion of impact, the amount of
energy generated during collision was determined. From this, a lower estimate of the velocity of
impact is roughly one half the speedof sound. [bib8] 8 These are precisely the effects expectedon
suspended particulates from cavitation-induced shockwaves in the liquid.
SECCCC01046.1.41.2 1.41.2 SONOLUMINESCENCE
secCCC01046.1.41.2.1 1.41.2.1 Types of Sonoluminescence
60 min. ultrasound
figCCC01046.3 Figure 3 The effect of ultrasonic irradiation on the surface morphology and particle size of Ni powder.
High-velocity interparticle collisions causedby ultrasonic irradiation of slurries are responsible for the
smoothing and removal of passivating oxide coating. Reproduced with permission.[bib9] 9
CCC01046.0070 In addition to driving chemical reactions, ultrasonic irradiation of liquids can also produce light.
Sonoluminescence was first observedfrom water in 1934 by Frenzel andSchultes. [bib15] 15 As with
sonochemistry, sonoluminescence derives from acoustic cavitation. It is now generally thought
that there are two separate forms of sonoluminescence: multiple-bubble sonoluminescence
(MBSL) andsingle-bubble sonoluminescence (SBSL). [bib11 bib12] 11,12 Since cavitation is a
nucleatedprocess andliquids generally contain large numbers of particulates that serve as nuclei,
the ‘‘cavitation field’’ generated by a propagating or standing acoustic wave typically consists of
very large numbers of interacting bubbles, distributed over an extended region of the liquid. If
this cavitation is sufficiently intense to produce sonoluminescence, then the phenomenon is
MBSL.[bib1 bib16] 1,16
CCC01046.0075 Under the appropriate conditions, the acoustic force on a bubble can be used to balance against
its buoyancy, holding the bubble stable in the liquid by acoustic levitation. This permits examination
of the dynamic characteristics of the bubble in considerable detail, from both a theoretical
andan experimental perspective. Such a bubble is typically quite small comparedto an acoustic
wavelength (e.g., at 20 kHz, the resonance size is approximately 150 mm). For rather specialized
but easily obtainable conditions, a single, stable, oscillating gas bubble can be forced into such
large-amplitude pulsations that it produces sonoluminescence emissions on each (and every)
acoustic cycle. Such SBSL is outside the scope of this chapter.

secCCC01046.1.41.2.2 1.41.2.2 Spectroscopic Probes of Cavitation Conditions
CCC01046.0080 The MBSL of both aqueous andnon-aqueous solutions is similar to the emission expectedfrom
high-temperature flames; e.g. excited-state OH from water, excitedstates of C2 (d 3
g -a 3 u,)
from hydrocarbons (these lines also give hydrocarbon flames their blue color), and CN excited
states in the presence of a nitrogen source. For both aqueous andnon-aqueous liquids, MBSL is
causedby chemical reactions of high-energy species formedduring cavitation by bubble collapse.
Its principal source is most probably not blackbody radiation or electrical discharge. MBSL is a
form of chemiluminescence.[bib16] 16
CCC01046.0085 Determination of the temperatures reachedin a cavitating bubble has remaineda difficult
experimental problem. As a spectroscopic probe of the cavitation event, MBSL provides a
solution. High-resolution MBSL spectra from silicone oil under Ar have been reported and
analyzed.[bib5] 5 The observedemission comes from excited-state C2 andhas been modeledwith
synthetic spectra as a function of rotational andvibrational temperatures. From comparison of
synthetic to observedspectra, the effective cavitation temperature is 5,050 150 K.
CCC01046.0090 A secondspectroscopic thermometer comes from the relative intensities of atomic emission
lines in the sonoluminescence spectra of excited-state metal atoms produced by sonolysis of
volatile Fe, Cr, andMo carbonyls. Sufficient spectral information about emissivities of many
metal atom excitedstates are available to readily calculate emission spectra as a function of
temperature. Because of this, the emission spectra of metal atoms are extensively usedby
astronomers to monitor the surface temperature of stars. From comparison of calculatedspectra
andthe observedMBSL spectra from metal carbonyls, another measurement of the cavitation
temperature was obtained.[bib6] 6 The effective emission temperature from metal atom emission
during cavitation under argon at 20 kHz is 4,900 250 K.
CCC01046.0095 The excellence of the match between the observedMBSL andthe synthetic spectra provides
definitive proof that the sonoluminescence event is a thermal, chemiluminescence process. The
agreement among these spectroscopic determinations [bib5 bib6] 5,6 of the cavitation temperature
andto that made by comparative rate thermometry of sonochemical reactions[bib4] 4 is extremely
good.
SECCCC01046.1.41.3 1.41.3 SONOCHEMISTRY
Sonochemistry 5
CCC01046.0100 In a fundamental sense, chemistry is the interaction of energy and matter. Chemical reactions
require energy in one form or another to proceed: chemistry stops as the temperature approaches
absolute zero. One has only limitedcontrol, however, over the nature of this interaction. In large
part, the properties of a specific energy source determine the course of a chemical reaction.
Ultrasonic irradiation differs from traditional energy sources (such as heat, light, or ionizing
radiation) in duration, pressure, and energy per molecule. The immense local temperatures and
pressures andthe extraordinary heating andcooling rates generatedby cavitation bubble collapse
mean that ultrasoundprovides an unusual mechanism for generating high-energy chemistry. Like
photochemistry, very large amounts of energy are introduced in a short period of time, but it is
thermal, not electronic, excitation. As in flash pyrolysis, high thermal temperatures are reached,
but the duration is very much shorter (by >10 4 ) andthe temperatures are even higher (by five- to
ten-fold). Similar to shock-tube chemistry or multiphoton infrared laser photolysis, cavitation
heating is very short lived, but occurs within condensed phases. Furthermore, sonochemistry has
a high-pressure component, which suggests that one might be able to produce on a microscopic
scale the same macroscopic conditions of high-temperature pressure ‘‘bomb’’ reactions or explosive
shockwave synthesis in solids. Control of sonochemical reactions is subject to the same
limitation that any thermal process has: the Boltzmann energy distribution means that the energy
per individual molecule will vary widely. One does have easy control, however, over the intensity
of heating generatedby acoustic cavitation using various physical parameters (including thermal
conductivity of dissolved gases, solvent vapor pressure inside the bubble, and ambient pressure).
In contrast, frequency appears to be less important, at least within the range where cavitation can
occur (a few hertz to a few megahertz), although there have been few detailed studies of its role.

6 Sonochemistry
secCCC01046.1.41.3.1 1.41.3.1 Homogeneous Sonochemistry: Bond Breaking and Radical Formation
CCC01046.0105 The chemical effects of ultrasoundon aqueous solutions have been studiedfor many years. The
primary products are H 2 andH 2O 2; there is strong evidence for various high-energy intermediates,
including HO2, H , OH .[bib17] 17 As one wouldexpect, the sonolysis of water, which
produces both strong reductants and oxidants, is capable of causing secondary oxidation and
reduction reactions, as often observed by Margulis and co-workers.[bib18] 18 Most recently there
has been strong interest shown in the use of ultrasoundfor remediation of low levels of organic
contamination of water.[bib19] 19 The OH radicals produced from the sonolysis of water are able
to attack essentially all organic compounds (including halocarbons, pesticides, and nitroaromatics)
and through a series of reactions oxidize them fully. The ultrasonic irradiation of organic
liquids creates the same kinds of products associated with very-high-temperature pyrolysis.[bib20]
20 The sonochemistry of solutes dissolved in organic liquids also remains largely unexplored. The
sonochemistry of metal carbonyl compounds is an exception. [bib21] 21 Detailedstudies of these
systems ledto important mechanistic understandings of the nature of sonochemistry. A variety of
unusual reactivity patterns have been observed during ultrasonic irradiation, including multiple
liganddissociation, novel metal cluster formation, andthe initiation of homogeneous catalysis at
low ambient temperature.[bib21] 21
secCCC01046.1.41.3.2 1.41.3.2 Applications of Sonochemistry to Materials Synthesis
CCC01046.0110 Of special interest is the recent development of sonochemistry as a synthetic tool for the creation
of unusual inorganic materials.[bib22] 22 As one example, the recent discovery of a simple sonochemical
synthesis of amorphous iron helpedsettle the long-standing controversy over its magnetic
properties.[bib23 bib24] 23,24 More generally, ultrasoundhas provedextremely useful in the
synthesis of a wide range of nanostructured materials, including high-surface-area transition
metals, alloys, carbides, oxides, and colloids.[bib22 bib25 bib26 bib27] 22,25–27 Sonochemical decomposition
of volatile organometallic precursors in high-boiling solvents produces nanostructured
materials in various forms with high catalytic activities. Nanometer colloids; nanoporous highsurface-area
aggregates; nanostructured carbides, sulfides, and oxides; and supported heterogeneous
catalysts can all be preparedby this general route, as shown schematically in [figCCC01046.4]
Figure 4. As an example, ultrasonic irradiation of Mo(CO) 6 produces aggregates of nanometersized
clusters of face-centered cubic molybdenum carbide, with high porosity and very large
surface area. The catalytic properties showed that the molybdenum carbide generated by ultrasound
is an active and highly selective dehydrogenation catalyst comparable to commercial
ultrafine platinum powder.[bib25] 25 In related work, Gedanken and co-workers have extended
the sonochemical synthesis of amorphous transition metals to the production of nanostructured
metal oxides simply by sonication in the presence of air.[bib26 bib27 bib28] 26–28
inorganic
support
oxygen
ULTRA-
hydrocarbon
SOUND
stabilizer
Sulfur
source
n = 100–1000
figCCC01046.4 Figure 4 Sonochemical synthesis of nanostructuredinorganic materials.

Sonochemistry 7
figCCC01046.5 Figure 5 Morphology of conventional andsonochemically preparedMoS2.
CCC01046.0115 The sonochemical synthesis of nanostructured molybdenum sulfide [bib29] 29 provides another
example of the utility of sonochemistry to the production of active catalysts. MoS2 is the
predominant hydrodesulfurization catalyst heavily used by the petroleum industry to remove
sulfur from fossil fuels before combustion. The sonochemical synthesis of MoS 2 by the irradiation
of solutions of molybdenum hexacarbonyl generates a most unusual morphology. As shown in
[figCCC01046.5] Figure 5, conventional MoS2 shows a plate-like morphology typical for such layered
materials, whereas the sonochemical MoS 2 exists as a porous agglomeration of clusters of
spherical particles with an average diameter of 15 nm. Despite the morphological difference
between the sonochemical andconventional MoS2, TEM images of both sulfides show lattice
fringes with interlayer spacings of 0.62 0.01 nm. The sonochemically preparedMoS2, however,
shows much greater edge and defect content, as the layers must bend, break, or otherwise distort
to form the outer surface. It is well establishedthat the activity of MoS2 is localizedat the edges
andnot on the flat basal planes. Given the inherently higher edge concentrations in nanostructuredmaterials,
the catalytic properties of sonochemically preparedMoS 2 shows substantially
increasedactivity for hydrodesulfurization.
CCC01046.0120 Using a very different route, Grieser and co-workers have sonochemically produced nanocrystalline
CdS colloids. [bib30] 30 In situ-generated hydrogen sulfide from the sonication of 2-mercaptopropionic
acid acted as the sulfiding agent. Spectroscopic studies revealed that sonication
produces CdS particles in the quantum dot range (‘‘Q-state’’, 3 nm diameter in this study) and
the sonication time and the thiol type determine the particle size distribution.
secCCC01046.1.41.3.3 1.41.3.3 Heterogeneous Sonochemistry: Reactions of Solids with Liquids
CCC01046.0125 The use of ultrasoundto accelerate chemical reactions in heterogeneous systems has become
increasingly widespread. The physical phenomena that are responsible include the creation of
emulsions at liquid–liquid interfaces, the generation of cavitational erosion and cleaning at liquid–
solid interfaces, the production of shockwave damage and deformation of solid surfaces, the
enhancement in surface area from fragmentation of friable solids, and the improvement of mass
transport from turbulent mixing andacoustic streaming.
CCC01046.0130 The use of high-intensity ultrasoundto enhance the reactivity of metal powders andsurfaces as
stoichiometric reagents has become an especially routine synthetic technique for many heterogeneous
organic andorganometallic reactions,[bib1 bib2 bib3] 1–3 particularly those involving reactive
metals such as Mg, Li, or Zn. This development originated from the early work of Renaud
andthe more recent breakthroughs of Luche. [bib3] 3 The effects are quite general andapply to
reactive inorganic salts andto main group reagents as well. Less work has been done with
unreactive metals (e.g., V, Nb, Mo, W), but results here are promising as well. Rate enhancements
of more than tenfold are common, yields are often substantially improved, and by-products

8 Sonochemistry
avoided. A range of synthetically useful examples of heterogeneous sonochemical reactions are
listedin [tblCCC01046.1] Table 1.
CCC01046.0135 The mechanism of the sonochemical rate enhancements in both stoichiometric andcatalytic
reactions of metals is associated with dramatic changes in morphology of both large extended
surfaces and of powders. As discussed earlier, these changes originate from microjet impact on
large surfaces andhigh-velocity interparticle collisions in slurries. Surface composition studies by
Auger electron spectroscopy andsputteredneutral mass spectrometry reveal that ultrasonic
irradiation effectively removes surface oxide and other contaminating coatings.[bib9] 9 The removal
of such passivating coatings can dramatically improve reaction rates. The reactivity of clean metal
tblCCC01046.1 Table 1 Some representative examples of heterogeneous sonochemistry.
Heterogeneous reagent Reactant Products
Compounds of metals
LiAlH4 Ar-X ArH
LiAlH4 R3M-X (X¼Cl, NR2,OR) R3M-H (M¼Si,Ge,Sn)
Al 2O 3 C 6H 5CH 2Br þ KCN C 6H 5CH 2CN
KMnO 4 RR 0 HCOH RR 0 CO
CrO2Cl2 RR 0 HCOH RR 0 CO
HBR2 R 0 2C¼CR 0 2 HR 0 2C-CR 0 2(BR2)
MS 2,V 2O 5 NR 3, py, Cp 2Co Intercalates
Hg
Mg
Li
Zn
Transition metals
(HR2BrC)2CO þ R 0 CO2H (HR2C)CO(C(O2CR 0 )R2)
(HR 2BrC) 2CO þ R 0 OH (HR 2C)CO(C(OR 0 )R 2)
R-Br R-MgBr
R2C¼CHCH2Cl þ Mg/C14H14 R2C¼CHCH2MgCl R-Br (R ¼ Pr, n-Bu, Ph) R-Li
R-Br þ R 0 R 00 CO RR 0 R 00 COH
R-Br þ (H3C)2NCHO RCHO
R3M-Cl (M¼C,Si,Sn) R3MMR3
R 2SiCl 2 (R ¼ arenes) cyclo-(R 2Si) 3
R2MCl2 þ Na þ Se (M¼Si,Sn) (R2MSe)3
CF3I þ RR0C¼O RR0C(OH)CF3 CnF2nþ1CO2H
CnF2nþ1I þ CO2
RR0C¼O þ BrCH2CO2R00 RR0C(OH)CH2CO2R00 PhBr þ RCOCH¼CHR0 þ Ni(acac) 2 RCOCH2CHR0Ph (R=H,alkyl)
RR 0 C¼O þ R 00 2C¼CHCH 2Br RR 0 (HO)CCR 00 2CH¼CH 2
MCl5 þ Na þ CO (M¼V,Nb,Ta) M(CO) 6
MCl6 þ Na þ CO (M¼Cr,Mo,W) M2(CO)10 2
MnCl3 þ Na þ CO Mn(CO)5
FeCl3 þ Na þ CO Fe(CO)4 2 þ Fe2(CO)8 2
Fe2(CO) 9 þ alkenylepoxide Fe(CO) 3( -allyllactone)
Fe2(CO)9 þ RHC¼CR0-CH ¼CHR0 Fe(CO)3( 4 -diene)
NiCl2 þ Na þ CO Ni6(CO)12 2
NiCl2 þ Na þ bipy þ COD/CDT Ni(bipy)(COD/CDT)
Co(acac) 3 þ C5H6 þ COD þ Mg/C14H10 Co(Cp)(COD)
RuCl3 þ Li þ 1,5-cyclooctadiene ( 6 -1,3,5-COT)( 4 -1,5-COD)Ru(0)
[Fe(C5R5)(CO)2]2 þ K þ Ph3C þ
Fe(C5R5)(CO)2(C2H4) þ
[M(C5R5)(CO) n] 2 þ K(M¼Fe,Ru,Mo) [M(C5R5)(CO) n]
Pd þ CH2¼CHCH2X [( 3 -H2C-CH-CH2)Pd(X)]2
La þ NH4SCN in HMPA La(NCS)3 4HMPA
Cu þ o-C6H4(NO2)I o-(O2N)H4C6–C6H4(NO2)

surfaces also appears to be responsible for the greater tendency for heterogeneous sonochemical
reactions to involve single electron transfer rather than acid-base chemistry.[bib31] 31
CCC01046.0140 Significant applications of sonochemistry to heterogeneous catalysis have also been noted. [bib32]
32 Among the more impressive results are hydrogenations and hydrosilations by Ni powder, Raney
Ni, andPdor Pt on carbon. For example, the hydrogenation of alkenes by Ni powder is enormously
enhanced(>10 5 -fold) by ultrasonic irradiation.[bib10] 10 This dramatic increase in catalytic activity is
due to the formation of uncontaminated metal surfaces from interparticle collisions caused by
cavitation-induced shockwaves.
SECCCC01046.1.41.4 1.41.4 CONCLUSIONS
CCC01046.0145 Since the early 1980 s, sonochemistry has become a well-defined technique for both mechanistic
and synthetic studies. The general details of the process of acoustic cavitation and the high-energy
chemistry generated during such bubble collapse are now reasonably well understood. The major
challenges that face a wider application of this technology include issues of scale-up and energy
efficiency. While laboratory equipment for sonochemical reactors are readily available commercially,
larger-scale apparatus is only now becoming commercially available. Perhaps more importantly,
sonochemistry shares with photochemistry an energy inefficiency that remains
problematic: while the production of ultrasound from electrical power can be extremely efficient,
the coupling of ultrasoundinto chemically useful cavitation events remains a low-yieldevent. As
we begin to understand the physics of cavitation clouds and dense multiphase acoustics, more
effective means of inducing cavitation in liquids may alleviate this current limitation.
1.41.5 REFERENCES
Sonochemistry 9
[bib1] 1. Crum, L. A.; Mason, T. J.; Reisse, J.; Suslick, K.S., Eds. Sonochemistry and Sonoluminescence, NATO ASI Series
C, v. 524; Kluwer: Dordrecht, The Netherlands, 1999.
[bib2] 2. Mason, T. J.; Lorimer, J. P. Sonochemistry: Theory, Applications and Uses of Ultrasound in Chemistry 1988, Ellis
Horword: Chichester, UK.
[bib3] 3. Luche, J.-L. Synthetic Organic Sonochemistry 1998, NewYork: Plenum.
[bib4] 4. Suslick, K. S.; Cline, Jr., R. E.; Hammerton, D. A. J.Am.Chem.Soc.1986, 108, 5641–5642.
[bib5] 5. Flint, E. B.; Suslick, K. S. Science 1991, 253, 1397–1399.
[bib6] 6. McNamara III, W. B.; Didenko, Y.; Suslick, K. S. Nature 1999, 401, 772–775.
[bib7] 7. Leighton, T. G. The Acoustic Bubble 1994, Academic Press: London.
[bib8] 8. Suslick, K. S.; Doktycz, S. J. Science 1990, 247, 1067–1069.
[bib9] 9. Suslick, K. S.; Doktycz, S. J. Adv.Sonochem.1990, 1, 197–230.
[bib10]10. Suslick, K. S.; Casadonte, D. J. J.Am.Chem.Soc.1987, 109, 3459–3461.
[bib11]11. Crum, L. A. Phys.Today 1994, 47, 22–29.
[bib12]12. S. J. Putterman, Sci.Am.1995, (Feb.), 46–52.
[bib13]13. LordRayleigh, Philos.Mag.Ser.6 1917, 34, 94–98.
[bib14]14. Richards, W. T.; Loomis, A. L. J.Am.Chem.Soc.1927, 49, 3086–3100.
[bib15]15. Frenzel, H.; Schultes, H. Z.Phys.Chem.1934, 27b, 421–424.
[bib16]16. Suslick, K. S.; Crum, L. A. Sonochemistry andSonoluminescence. In Encyclopedia of Acoustics; Crocker, M. J.,
Ed., Wiley-Interscience: New York, 1997; Vol. 1, pp 271–282.
[bib17]17. Riesz, P. Adv.Sonochem.1991, 2, 23–64.
[bib18]18. Margulis, M. A.; Maximenko, N. A. Adv.Sonochem.1991, 2, 253–292.
[bib19]19. Destaillats, H.; Lesko, T. M.; Knowlton, M.; Wallace, H.; Hoffmann, M. R. Ind.Eng.Chem.Res.2001, 40,
3855–3860.
[bib20]20. Suslick, K. S.; Gawienowski, J. W.; Schubert, P. F.; Wang, H. H. J.Phys.Chem.1983, 87, 2299–2301.
[bib21]21. Suslick, K. S. Adv.Organomet.Chem.1986, 25, 73–119.
[bib22]22. Suslick, K. S.; Price, G. Annu.Rev.Mater.Sci.1999, 29, 295–326.
[bib23]23. Suslick, K. S.; Choe, S. B.; Cichowlas, A. A.; Grinstaff, M. W. Nature 1991, 353, 414–416.
[bib24]24. Grinstaff, M. W.; Salamon, M. B.; Suslick, K. S. Phys.Rev.B 1993, 48, 269–273.
[bib25]25. Hyeon, T.; Fang, M.; Suslick, K. S. J.Am.Chem.Soc.1996, 118, 5492–5493.
[bib26]26. Cao, X.; Prozorov, R.; Koltypin, Y.; Kataby, G.; Felner, I.; Gedanken, A. J.Mater.Res.1997, 122, 402–406.
[bib27]27. Shafi, K. V. P. M.; Koltypin, Y.; Gedanken, A.; Prozorov, R.; Balogh, J.; Lendvai, J.; Felner, I. J.Phys.Chem.
B. 1997, 101, 6409–6414.
[bib28]28. Kataby, G.; Prozorov, T; Koltypin, Y.; Cohen, H.; Sukenik, C. N.; Ulman, A.; Gedanken, A. Langmuir 1997, 13,
6151–6158.
[bib29]29. Mdleleni, M. M.; Hyeon, T.; Suslick, K. S. J.Am.Chem.Soc.1998, 120, 6189–6190.
[bib30]30. Sostaric, J. Z.; Carusohobson, R. A.; Mulvaney, P.; Grieser, F. J.Chem.Soc.Faraday Trans.1997, 93,
1791–1795.
[bib31]31. Luche, J.-L. Ultrasonics Sonochem. 1994, 1, S111.
[bib32]32. Suslick, K. S. In Handbook of Heterogeneous Catalysis; Ertl, G.; Knozinger, H.; Weitkamp, J., Eds.; Wiley-VCH:
Weinheim, 1997; Vol. 3, pp 1350–1357.